Nitration of-alkanes



Patented Aug. 24, 1943 UNITED STATES NITRA'EION F ALKANES Edward d e, Terr Haute, Ind... assisno to Comm rcia dolvents C poration. 'Eo ro Hauta i Ind. a corporati n f Ma yland No Drawing. Application Au ust 2. 1949, Serial N 0. 350,153

2 Claims. (01. 260-644) My invention relates to the nitration of alkanes, and more specifically to an improved method of controlling the reaction in the direct vapor phase nitration of alkanes.

The direct vapor phase nitration of alkanes is disclosed in if. 8. Pat. 1,967,667 of B. Hass et ai., U. S. Pat. 2,071,122 of H. B. Hass et 8.1., U. S. Pat. 2,161,475 of G. K. Landon, U. 5. Pat. 2,164,774 of G. K. Landon, and U; S. Pat. 2,206,813 of H. B. Hass et al. In this process an alkane and nitric acid, or nitrogen dioxide, are reacted in the vapor phase to. produce nitrm-aikanes. While. satisfactory yields and conversions are obtainable by this Process, the Over-all yields and conversions obtained. in a continunu process, have not equaled the hi h instantaneous yields nd conversions Whiohare often secured.

I ha e und that the reason ior this failure to ob ain uniform resu ts in carryin out this eaction. is the inadcouacy of o dinary control measures- :If the react on ap ears to be ope a-t nc at pt mum efiio en y with an pa t o 1 combination of action conditions emoeratu contact tim pr sure. c m sition o reacion mixture). careful m intenan e of these re ac ion conditions will not result in u iform operation .I have now io-und. however, hat subst ntially ni orm ope a ion ca be scoured i the me t mp ratu e actor. (i. cont ct time and/ r tem er ture r mother word-s. the uantum ct hoot nput is roeu e ed'so as to maintain thee iditr f the roa tionproduot hin a elatively arr w sa e-a disco water one-o t o r action products of henit at on react on. a d t e n tr allsanes are n. a l ases at lea par al y immis o with ater. the iquid r action product se arate. int wo layers- I rata e acidity o the aqueous layer constitutes a convenient measure of acidity of the reaction products, and this value may be used as the basis for the control of the time-temperature factor in accordance with my present invention.

In the vapor phase nitration of alkanes, as in other vapor phase reactions, the contact time and reaction temperature are interrelated so that increased reaction is obtainable by increasing either or both of these factors. It is to be understood, therefore, that when the phrase regulating the time-temperature factor is used herein, it is meant to signify regulation of the contact time, and/or the reaction temperature.

If the acidity of the aqueous layer of the reaction products rises above the desired operating range, the reaction temperature should be increased, .or the contact time increased (space eloc ty dec eased. or oth o thes changes may be made simultaneously- Similarly, i he acidity of the aqu ous la r ro s below h sired operat n range, the rea tion em erat e should b decr a ed or t e conta t-time sh be decreased (spa evelooi y in reas d or bo o the e changes "may e made s mu aneously. Since it is usuall desirable to operat at constant pace velooityr t s mo t onv nie t m ely to adju the react n temperatur in ac rdance w th th ac di y ofthe aqueous layer- Ver smal adi stmentslin tem era ure wil use relivoly largo fluctu ti ns o th acidity. a d the.

empe ature .adiustmon shou d. h r fo he made radua1 .v A tempe atu e chan e; o 5 s. usua ly sumo on to produce a cidity utside of the desired operating range, dnd-tlllisresult in lowered yield and conversion.

I have found that for the nitration of any of the alkanes, the acidity of the aqueous layer of the product (expressed'in normality), should be maintained within the range 0.1' N to 1.5 N. The optimum value within this range, in any given case, will depend upon the particular alkane being nitrated, and on the composition of the reaction mixture. The optimum acidity decreases with increasing watercontent of the reaction mixture. Thus, if nitric acid is used as' -the nitrating agent, the optimum operating acidity will be lower when dilute acid is used, than when concentrated acid is used.

My invention is particularly applicable to the n ra ion. o elite nos con. as from two to four arbon atoms. When n ra in these a s-a-ne u ng nit ic ac as t e .ni ratine a ent. the acidity of the aqueous la e of th products is ui ably maintained within he ran e o e-9.16 N. f th rea ion mixture consist so el of alkan and concent ated nitr aoid. the ac di y is: pr

erably maintained in the upper portion of this range. With additional Water present in the reaction mixture, the acidity is preferably maintained in the lower part of this range. When nitrating methane the acidity of the aqueous layer of the products is maintained at a higher value than required for the nitration of other alkanes. I prefer to maintain the acidity at 0.7-1.0 N. when nitrating methane with concentrated nitric acid. Somewhat lower acidity is preferable if more water is present in the reaction mixture.

A determination of yield and conversion when operating at substantially constant acidity, for different acidity values within the operating ranges specified above, will, of course, constitute the best method for determining the optimum value in any given case. It is generally desirable to attempt to maintain the acidity within 0.1 N above or below the value thus determined.

Except for the improved method of controlling the reaction described above, the nitration may be effected in accordance with prior practices. The usual ratios of reactants may be employed, and the reaction may be carried out under variious conditions of pressure, temperature, and space velocity known to be suitable for an particular reaction mixture. The initial values of temperature and space velocity thus chosen, however, will be modified as required by the acidity; i

when carrying out my process.

My invention may be further illustrated by the following specific examples:

Example I Nitric acid was vaporized and mixed with propane to form a mixture of nitric acid vapor, propane and Water vapor, in molar ratios of approximately 1.0 to 5.0 to 2.7. This mixture was passed through a heated reaction tube at a gauge pressure of 80 lbs. per sq. in., and a space Velocity of approximately 5000 liters of gas. calculated at C. and 760 mm., per liter of reaction space, per hour. The reaction chamber was surrounded by a bath of molten salt and the'temperature of the salt bath was adjusted in accordance with the acidity of the aqueous layer of the reaction products. Minor adjustments in temperature within the range 386-391 C. were necessary to maintain the acidity within the range 0.3-0.5 N. When the acidity was maintained in this range the conversion of nitric acidto nitroparaflins was approximately 40 per cent.

Example II Nitric acid vapor, propane, and water vapor were passed through a heated reaction tube in molar ratios of approximately 1.0 to 4.8 to 7.6, at a space velocity of 19 thousand and a gauge pressure of 125 lbs. per sq. in. In this case temperature adjustments inthe range 400-403 C. were found to be necessary to maintain the acidity in the range 0.1 to 0.3 N. When the acidity was maintained in this range the conversion of nitric acid to nitroparafiins was approximately 40 per cent.

Example III Nitric acid vapor, butane, and water vapor were passed through a heated reaction tube in molar ratios of approximately 1.0 to 4.7 to 2.1, at a space velocity of approximately 25 thousand and a gauge pressure of *lbs. per sq. in. In this case temperature adjustments in the range 498- 503 C. were found to be necessary to maintain the acidity in the range 0.4-0.6 N. When the acidity was maintained in this range, the conversion of butane to nitroparafiins was approximately 44 per cent.

Example IV Nitric acid vapor, methane, and water vapor in molar ratios [of approximately 51.0 {E1101 12.0 to 2.1 were passed through" a heatedraction tube at a pressure of 80 lbs. per sq. in. (gauge), and

- a space velocity of 14 thousand. The temperature was regulated to maintain the acidity of the aqueous layer of the products within the range 0.7-1.0 N. The conversion of nitric acid to nitromethane was approximately 18 per cent.

It is to be understood, of course that the above examples are merely illustrative, and do not limit 1 the scope of my invention. Various other combinations of reaction conditions may be employed, as long as the time-temperature factor is regulated in accordance with the acidity'of the products. Any of the other ,alkanes.may"be;nitratetl,

and nitrogen dioxide maybe usedin place-".01" nitric acid, as illustrated in theexamplesr :';In

general it may be said that the use of any equivalents or any modifications ofprocedure, which would occur toone skilled in theart, is includedin the scope of my invention.

My invention now having been described, what Iclaimis: i

1. A process for controlling thereaction in the production of nitro-alkanes which comprises continuously passing'an. alk'ane and nitric acid in the vapor stage through a heated reaction zone, condensing the reaction product to produce a layer of nitro-alkan'e and a layer of water, the latter containing unreacted nitric a'cidand controlling the reaction by continuouslyregulating, during the reaction, the quantity of" heat 'input' within a range that will maintain the acidity'of the aqueous layer at a substantially constant value which is'be'tween 0.1- N to-1 .5 l \T-to secure substantially'uniform operation." 2. A process for controlling the reaction in the production of nitro-alkanes which comprises continuously passing an' alkane and nitric acid 'in the vapor stage through a heated reaction zone, condensing the reaction productto produce alayer of nitro-alkane and a 'la'yer'of water) the latter containing un'reacted nitric-acid'and om" trolling the reaction by continuously regulating} during the reaction, thequantity or heat ifnput within a range that will maintain the acidity-of the aqueous layer at 'a substantially constant value which is between 0.1 N 7 to 1.5 N to secure 

